Field of the Invention
The present invention relates to a technology for a scanning microscope and particularly relates to a technology for a scanning microscope that includes a varifocal lens.
Description of the Related Art
Scanning microscopes such as confocal laser scanning microscopes and multiphoton-excitation laser scanning microscopes are known as apparatuses for observing a three-dimensional image of an object.
For directions orthogonal to the optical axis of an objective (x direction and y direction), a scanning microscope is capable of performing a scan at a high frequency of hundreds to thousands Hertz using a galvanometer scanner or a resonance scanner. Meanwhile, a scan in an optical-axis direction (z-axis direction) is performed by moving the objective or a stage in the optical-axis direction typically using a piezoelectric transducer (hereinafter referred to as a piezo element) and another actuator. U.S. Pat. No. 8,553,324 describes a technique for achieving a scan in an optical-axis direction by moving a tube lens in the optical-axis direction.
However, a method of mechanically moving structures such as an optical system and a stage using an actuator involves a time for the moving and a time before oscillations caused by the moving stop. Hence, it is difficult to perform a fast scan in an optical-axis direction. As a result, it takes a longtime to obtain a three-dimensional image.
Japanese Laid-open Patent Publication No. 2004-317704 describes a varifocal lens as means for solving such a technical problem. Use of the varifocal lens allows a focal length to be rapidly changed by changing an applied current or voltage. This enables a fast scan in an optical-axis direction. Recently, varifocal lenses have been developed that vary a focal length more greatly than those in the prior art. Hence, usability of a varifocal lens as scan means has been enhanced.